\documentclass[12pt]{article}
\pagestyle{empty}
\begin{document}

\begin{displaymath}
\int H(x,x')\psi(x')dx' = -\frac{\hbar^2}{2m}\frac{d^2}{dx^2}
                          \psi(x)+V(x)\psi(x)
\end{displaymath}

\end{document}
